Different kinds of sinusoidal oscillators are known, for instance negative resistance oscillators, feedback oscillators, phase-shift oscillators, resonance oscillators.
The present invention concerns a resonance sinusoidal oscillator, suitable for low frequency applications, in which the resonant circuit comprises a conventional capacitive element whereas the inductive element is formed by an active electric two-terminal network which has no coil or magnetic core and comprises only operational amplifiers, resistors and capacitors.
As a low frequency oscillator is of interest, such a two-terminal network cannot be a resonant cavity or a helicoidal resonator or any other kind of distributed-parameter electromagnetic resonator. Also piezoelectric and magnetostrictive resonators cannot be employed, so that the known technique makes use of LC oscillators in which the oscillation frequency is given by the relation: ##EQU1##
If a frequency variable within a wide range of relatively low values (for instance a frequency below 20 kHz) is to be obtained, it is not a practical solution to vary the value of L and C while keeping within acceptable limits the component size; also, it is not suitable to use in the circuit varactor diodes whose capacitance, variable depending on the control voltage, is of few picofarads.